To improve communication capabilities, wireless communication systems may be configured for multiple-input multiple-output (MIMO) communications. MIMO systems employ two or more antennas for both transmission and reception. By utilizing multiple antennas, MIMO systems may improve wireless communications by providing signal diversity, and/or channel diversity. MIMO signals that enhance signal diversity are particularly useful in cellular wireless networks, where the landscape often makes line of sight transmission impractical.
In cellular networks, MIMO signals can be encoded using space-time coding, which is sometimes referred to as a diversity coding or Alamouti coding, to improve signal diversity. To transmit a signal encoded using space-time coding, a transmitting device transmits the same signal stream from multiple antennas. Further, the signal streams may be orthogonally coded in relation to each other. A receiving device with multiple antennas (preferably corresponding in number to the antennas of the transmitting device) may then receive the signal from multiple streams transmitted from the multiple antennas of the transmitting device. Such a configuration may result in signal gain at the receiving device.
MIMO systems may also employ spatial multiplexing to increase channel capacity. To employ spatial multiplexing, a high data rate signal may be divided into multiple signal streams. Each of these unique streams may then be transmitted on the same RF frequency from multiple antennas of a transmitting device and received by multiple antennas of a receiving device. Spatial multiplexing may be particularly helpful in communication channels with higher signal-to-noise (SNR) ratios to enable higher throughput than would be possible without this MIMO technique.